The present invention is directed to a liquid crystal cell with two carrier plates, which enclose between them a liquid crystal layer which can be switched by areas between optically different states with the liquid crystal layer having different oriented strip-like zones at least in a switchable area at least adjacent one of the two parallel boundary surfaces for the cell and methods of operating the device as well as methods for producing the device.
An article by Rupert Chabicovsky and Gerhard Kocmann, "Liquid-Crystal Cells With Special Electrodes For The Generation Of Uniform Colors By Optical Birefringence", IEEE Transactions on Electron Devices, Vol. ED 24, No. 7, July 1977, pp 807-810 discoses a liquid crystal cell, which had been treated in a special way so that all of the homeotropic molecules are pretilted in the same desirable direction. To accomplish this pretilting, the surface of the carrier plate forming the layer has been provided with a wave-shaped profile and one or more of the flanks of the crest of the profile are treated to orient the molecules of the layer in a different manner so that the coaction between the orientations causes the desired tilting. While the profile surface may have strips on the flanks of the crest which are different orientation materials, these materials are selected so that the entire layer is tilted in the same direction at the same angle.
In standard liquid crystal displays, the turn-on time t.sub.1 depends on the electrical field E with t.sub.1 being approximately equal to 1/E.sup.2 and the turn-off time t.sub.2, which is normally longer, will depend on the thickness d of the liquid crystal layer with t.sub.2 being approximately equal to d.sup.2. Because of this interrelationship, attempts have now been made to shorten the switching time of a liquid crystal cell primarily by reducing the spacing between the carrier plates. This solution for shortening the switching times has not been too satisfactory. Because the substrates are never entirely flat and seldom inherently stable, there is an increasing tendency of short circuits and due to the unavoidable interval support tolerances, liquid crystal layers with fixed thickness of approximately 5 .mu.m can only be realized and produced with the greatest care and the smallest thickness value appears to be approximately 3 .mu.m.
Another attempt to improve the switching behavior of a liquid crystal cell is by use of electrode systems in which interdigital electrodes are provided so that fields can be applied parallel to the layer surface. Discussions of these types of systems are contained in an article by D. J. Channin, "Triode Optical Gate: A New Liquid Crystal Electro-Optic Device", Applied Physics Letter, Vol. 26, No. 11, June 1, 1975, pp. 603-605. Since the liquid crystal now no longer relaxes into its initial position but rather is rotated back by means of the application of electrical field, the turn-off times can indeed be reduced. However, the minimum interval between neighboring electrodes of an interdigital electrode structure, which can be attained with a standard photo-etching technique, is approximately 50 .mu.m so that the "triode" concept requires high switching voltages and can only be minimally employed in multiplexable displays.